What one needs to remember in planning rehabilitation after cruciate ligament surgery is that every single graft used today, whether natural or synthetic, from your own body or someone else's, lacks a blood supply when it is inserted during surgery.
The first period of rehabilitation concentrates on preventing the formation of adhesions (internal scars) inside the knee by passive range-of-motion exercises and efforts to minimise inflammation. While still in bed active work will focuses on keeping strength in the quads muscle as it is so very sensitive to early inhibition. Once up and about initially only gentle active work will be allowed.
As rehabilitation progresses, attention will focus initially on regaining range-of-motion. Strength and endurance training will come later, and there will also be later emphasis on re-educating the leg with balance exercises.